Washing machine appliances can use a variety of fluid additives (in addition to water) to assist with washing and rinsing a load of articles. For example, detergents and/or stain removers may be added during wash and prewash cycles of washing machine appliances. As another example, fabric softeners may be added during rinse cycles of washing machine appliances.
Fluid additives are preferably introduced at an appropriate time during the operation of washing machine appliance and in a proper volume. By way of example, adding insufficient volumes of either the detergent or the fabric softener to the laundry load can negatively affect washing machine appliance operations by diminishing efficacy of a cleaning operation. Similarly, adding excessive volumes of either the detergent or the fabric softener can also negatively affect washing machine appliance operations by diminishing efficacy of a cleaning operation.
For instance, when too much detergent is added during a wash cycle, detergent can remain in articles after a rinse cycle because the rinse cycle may not be able to remove all of the detergent from the articles. Unremoved detergent can cause graying within such articles as the detergent builds up over time, can contribute to a roughness feeling of such articles, and can trigger skin allergies. The unremoved detergent can also negatively affect the efficacy of fabric softener during the rinse cycle. Further, unremoved detergent can also cause excess suds that can damage the washing machine and/or decrease a spin speed of the washing machine appliance's drum thereby causing articles therein to retain excessive liquids.
As a convenience to the consumer, certain washing machine appliances include systems for automatically dispensing detergent and/or fabric softener. Such systems can store one or more fluid additives in bulk and dispense such fluid additives during operation of the washing machine appliances. However, accurately dispensing a particular volume of fluid additive with such systems can be difficult. For example, certain washing machine appliances utilize a pressure sensor to determine the amount of additive inside a bulk tank before and after each individual dispense and then calculate dosing amounts. Utilizing pressure sensors to determine the amount of fluid additive dispensed from the bulk tank can be problematic. For example, the pressure sensors add to an overall cost of the washing machine appliance.
Current bulk tanks also make accurately dispensing a specific volume of fluid additive difficult. For example, bulk tanks in certain washing machine appliances are at least thirty inches tall. Thus, a priming time for the bulk dispense system can vary greatly because the priming time can be directly proportional to a height of fluid additive within the bulk tank. When the bulk tank is full, the priming time is shorter because the fluid additive is very close to a pump of the bulk dispense system. When the bulk tank is almost empty, the priming time is longer because the fluid additive has to travel further vertically, i.e., from almost the bottom of the bulk tank to the pump.
Accordingly, a washing machine appliance with features for accurately dispensing a volume of fluid additive would be useful.